RU2534594C2 - Perfected process of investment wax pattern production of turbomachine blade assembly, metal mould and wax pattern to this end - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy. Wax pattern (50) of turbomachine stator circular blade assembly comprises radially inner and outer coaxial shields (52) and (54) interconnected by blades (56), one of the latter (58) having inner cavity. To get wax patter, metal core (40) is arranged in metal mould to make the image of blade cavity (18), wax injected into the mould to withdraw wax patter with core (40) therefrom. Said core is arranged in said mould so that its radially inner end is located at mould section (58) that makes blade with cavity at a distance from radially inner end (52) of said mould section.

EFFECT: decreased amount of rejects.

7 cl, 7 dwg

Description

Technical field

The present invention relates to the manufacture of an annular blade stator assembly for a turbomachine, such as an aircraft turbomachine.

Figure 1 schematically shows such a blade assembly 10, sometimes called the front or rear guide vane assembly, depending on its function in the turbomachine. This blade assembly 10 typically includes two coaxial ring structures or screens that are respectively internal 12 and external 14 and which are connected to each other by a plurality of blades 16.

More specifically, the invention relates to the manufacture of a blade assembly comprising at least one blade 18, containing a cavity, mainly elongated in the radial direction, intended, for example, to measure physical parameters, such as pressure and temperature of air moving along the blade, possibly through the holes 20 of this blade.

State of the art

The blades of the stator assemblies of turbomachines are usually made by a lost-wax casting method, in which a wax model is preliminarily made having the shape of a blade assembly to be made, which further provides the production of a cement mold by molding to duplicate this wax model. After the wax has been removed, a metal alloy is cast into the previously obtained cement mold to form, after cooling and removing from the mold, the desired blade assembly.

The wax model is made in advance by means of a metal mold having approximately the shape of the blade assembly to be made.

If at least one blade of the blade assembly contains a cavity, an elongated casting core, which is shown in FIG. 2, is inserted into the metal mold section that forms the aforementioned blade in order to form an impression of the cavity. This rod 22 is made of ceramic material, so that it has sufficient heat resistance to withstand the high temperatures associated with the casting of the aforementioned metal alloy, and to ensure subsequent removal of this rod by the usual chemical method.

Then, wax is injected into the metal mold containing the casting rod under pressure in order to form, when it cools, a model of the manufactured blade assembly in which the casting rod is surrounded by wax and occupies a space corresponding to the aforementioned cavity.

During wax injection, the casting bar is mounted on a metal mold so that it is firmly held in place in order to effectively limit the risk of the bar deforming under the pressure of the wax, which can reduce the accuracy of the geometric shape of the wax model and, as a result, the blade assembly obtained on the final stage of the manufacturing method. The foundry core is usually held in place by two protrusions 24 and 26 (FIG. 2) formed respectively at both ends of the core and protruding from the metal mold, allowing them to be gripped by appropriate support means.

Then, a cement mold is made by molding to duplicate the wax model obtained previously and containing the rod, so that cement surrounds both protrusions of the rod, which extend beyond the wax model. After this cement has hardened and after removing the wax, a cement mold is obtained containing a core, which is now held in place by the cement mold itself.

Then, after pouring the metal alloy into the previously obtained cement mold and after cooling the metal alloy, the rod is removed, usually by a chemical method, and the obtained metal part is removed from the mold to obtain an annular blade assembly.

Removing the rod leaves an opening 28 in the inner screen of this blade assembly formed as a result of the passage of one of the protrusions of the rod, which is shown in FIG. 3. Since the presence of a hole in a given location is undesirable, this hole is usually sealed with brazing or a similar method.

However, this hole sealing operation increases the cost of manufacturing annular blade assemblies.

In addition, the presence of soldered parts in the internal screens of these nodes causes a violation of the shape and structure in these screens, which are such that they reduce the mechanical strength and, accordingly, the service life of these screens.

In addition, in some cases, the casting core may undergo deformation under the pressure of the wax, with the injection of the latter, which leads to the appearance of expensive waste.

Description of the invention

Thus, one aim of the invention is to provide a simple, cost-effective and efficient solution to these problems.

To achieve this goal, a method for manufacturing a wax model of an annular blade assembly of a stator of a turbomachine, designed to manufacture the shape of a given blade assembly, said model includes two coaxial screens, respectively radially internal and radially external, which are connected to each other by a plurality of blades, of which at least one contains an internal cavity, said method comprising, sequentially, using a metal mold having approximately the form to be given to said model of the ring blade assembly:

- the placement of the casting rod, made with the possibility of imprinting the aforementioned cavity, in the area of the aforementioned metal mold, which forms a blade containing a cavity, the aforementioned rod having a predominantly elongated shape containing a radially external end mounted in a metal form;

- injection of wax into a metal mold containing the aforementioned rod;

- after cooling the wax, removing the resulting wax model containing the core from the mold.

In accordance with the invention, the aforementioned rod is made of metal and is positioned so that its radially inner end is placed on a section of the mold forming a blade containing said cavity at a distance from the radially inner end of this section of the mold.

The use of a metal rod, which is more rigid compared to a commonly used ceramic rod, allows this rod to be installed on a metal mold only with its radially external end, while minimizing the risks that this rod will undergo deformation during wax injection. This installation of the rod on a metal mold is particularly preferred when the wax model made by this method is used in a method for manufacturing an annular blade assembly, as will be described in more detail below.

The increased strength of the rod means that it is possible to increase the injection pressure of the wax and to reduce the percentage of wax patterns that turn out to be defective due to the deformation of the rod.

The invention also relates to a method for manufacturing an annular blade assembly of a stator of a turbomachine, comprising two coaxial screens, which are respectively radially internal and radially external, connected to each other by a plurality of blades, of which at least one contains an internal cavity, said method comprising sequentially:

- the manufacture of a wax model of the annular scapular node by the method of the type described above;

- manufacturing a mold from a heat-resistant material by molding to duplicate the aforementioned wax model, followed by removal of the wax;

- casting a molten metal alloy in a mold made of a heat-resistant material containing the aforementioned rod to form said annular blade assembly;

- after cooling the metal alloy, removing the annular blade assembly from the mold and removing the rod.

Thus, this method of manufacturing an annular blade assembly uses the above-described method of manufacturing a wax model, in which the rod is mounted on a metal mold with only one of its radially outer ends.

After completing the steps of duplicating the wax model and removing wax, the radially outer end of the rod is enclosed in a hardened heat-resistant material and, therefore, allows the rod to be connected to a mold made of this material, while the radially inner end of the rod continues inside the mold, at a distance from the radially inner the end of the section of this mold, forming a blade containing the aforementioned cavity, and, accordingly, at a distance from the radially inner screen of the mold.

As a result, the radially inner end of the rod does not form a hole in the inner screen of the annular blade assembly obtained by this method. And therefore, it is no longer necessary to carry out the operation of closing the holes in this internal screen, which allows to reduce the cost of manufacturing annular blade assemblies of stators of turbomachines and increase the service life of these assemblies.

Preferably, before manufacturing a mold from a heat-resistant material, a method of manufacturing an annular blade assembly of a stator of a turbomachine also includes removing said metal rod from said wax model and then placing a rod of the same shape made of ceramic material in a print formed in wax by said metal rod.

The rod made of ceramic material has high heat resistance and is therefore more suitable for the subsequent stage of pouring molten metal alloy. Moreover, at the final stage of this method, the ceramic rod can be removed by the usual chemical method.

The metal rod preferably has a cross section that tapers towards its radially inner end.

The tapered shape of the metal bar makes it easier to remove from the wax model, while reducing the risk of damage to the model. The strength of this metal rod also allows you to limit the risks of damage to the rod when it is removed.

If the metal rod is replaced with a ceramic rod, as described above, the latter has the same shape as the metal rod, and the narrowing of this shape facilitates the insertion of this ceramic rod into the impression (cavity) previously formed by the metal rod.

However, the method in accordance with the invention can be implemented without performing the aforementioned step of replacing the rods, especially when the metal forming the metal rod has a sufficiently high melting temperature compared to the melting temperature of a metal alloy poured into a mold made of heat-resistant (or refractory) material, to allow the metal rod to withstand pouring of the alloy without the risk of melting the rod.

The invention also relates to a metal mold intended for the manufacture, by the method of the type described above, of a wax model of an annular blade assembly of a turbomachine stator including two coaxial screens, respectively radially internal and radially external, which are connected to each other by a plurality of blades, of which at least one contains an internal cavity, and the said shape includes in the area that forms the said blade containing the cavity, the foundry core a long shape containing a radially outer end mounted on a metal mold to form an imprint of the cavity, said shape being characterized in that the rod is made of metal and arranged so that its radially inner end is placed on said mold portion forming a blade containing said cavity , at a distance from the radially inner end of said mold portion.

The invention also relates to a wax model for manufacturing, by the method of the type described above, an annular blade assembly of a stator of a turbomachine including two coaxial screens, respectively radially internal and radially external, which are connected to each other by a plurality of blades, of which at least one contains the internal cavity, and the said shape includes in the area that forms the said blade containing the cavity, the casting rod is mainly elongated, soda holding a radially outer end protruding from the model to form an imprint of the said cavity, said model being characterized in that the rod is made of metal and is positioned so that its radially inner end is placed on the said part of the model forming a blade containing the said cavity at a distance from the radially inner end of said portion of the model.

Brief Description of the Drawings

The invention will be better understood and other details, advantages and characteristics of it will become apparent after reading the description below, presented as a non-limiting example and with reference to the accompanying drawings, in which:

Figure 1 shows the previously described perspective view of the annular blade assembly of the stator of a turbomachine of a known type;

Figure 2 shows the previously described perspective view of a rod of a known type for manufacturing the blade assembly shown in figure 1;

Figure 3 is a partial schematic view of the inner screen of the annular blade assembly shown in figure 1, before sealing the hole formed by the shaft shown in figure 2;

Figure 4 is a flowchart showing the main steps of the method in accordance with the invention for manufacturing an annular blade assembly of a stator of a turbomachine;

Figure 5 is a perspective schematic view of a rod for implementing the method in accordance with figure 4;

FIG. 6 is a partial perspective view of a wax model of an annular blade assembly in which the shaft shown in FIG. 5 is mounted;

Fig.7 is a view similar to Fig.6, with a cross section.

Detailed Description of Preferred Embodiments

The flowchart shown in FIG. 4 illustrates a method in accordance with the invention for manufacturing an annular blade assembly of a stator of a turbomachine of the same type as the blade assembly shown in FIG. 1 and accordingly including two coaxial screens, respectively, an inner 12 and the outer 14 connected to each other by a plurality of blades 16, of which at least one blade 18 has a cavity.

This method includes four consecutive main steps, respectively indicated by reference numerals 30, 32, 34 and 36 in the flowchart shown in FIG. 4.

The first step 30 consists of manufacturing in the usual way the metal mold of the manufactured blade assembly; the second step 32 consists of making a wax model of the blade assembly using a given metal mold; the third step 34 consists of making a mold of cement or any suitable heat-resistant material in general by duplicating the wax model; and the fourth step 36 consists of manufacturing a blade assembly by means of the aforementioned cement mold.

More specifically, the second step 32 includes a step 38 of placing in the metal form of the rod, which differs from the conventional rod shown in figure 2, in that it is made of metal, such as steel, and in that it does not contain a protrusion at its end designed to be placed radially at the inside of the mold.

Figure 5 shows a rod 40 of this type and, in particular, its end 42, which is designed to be placed radially at the outer part of the mold and which contains a protrusion 44 similar to the protrusion 24 of the rod of the conventional type shown in figure 2, and its end 46, which is designed to be placed radially at the inside of the mold and which does not contain a protrusion. This rod 40 has a cross section that tapers towards its aforementioned end 46, as shown in FIG. 5, which is made possible, in particular, by the absence of a protrusion at this end.

In the aforementioned step 38 (FIG. 4), the rod 40 is mounted on a portion of the metal mold forming the blade of the blade assembly that contains the cavity so that the protrusion 44 of the end 42 of the rod extends beyond the mold, passing through a wall opening of the mold forming a radially external screen the blade assembly, and so that the other end 46 of the rod extends inside the mold, at a distance radially inward from the wall of the mold, forming the radially inner screen of the blade assembly.

The next step 48 of the second step 32 of the method consists in injecting the wax under pressure into a metal mold containing the above-described metal rod 40, in the usual way, until the mold is filled with wax, while the rod is enclosed in wax, except for its protrusion, which stands for the limits of the metal form. The strength of the metal rod protects the latter from deformation during the injection of wax, despite the pressure exerted on the rod by this wax.

After cooling, the hardened wax forms a model 50 of the manufactured annular blade assembly, which is shown in FIGS. 6 and 7. This model 50 has approximately the shape of an annular blade assembly and, accordingly, includes coaxial screens, respectively, inner 52 and outer 54, and many blades 56, connecting these two screens, and includes a blade 58, configured to form a blade of the blade assembly, which contains a cavity, and this blade 58 of the wax model is a blade that contains the rod 40 lives. Fig. 7 shows, in particular, the position of the radially inner end 46 of the rod 40, which is located at a distance radially inward from the radially inner shield 52, which forms the radially inner end of the blade 58.

In a preferred embodiment of the method in accordance with the invention, the second step 32 of this method continues at step 60, which consists in removing the metal rod 40 from the wax model and replacing it with a rod of the same shape made of ceramic material and, therefore, having increased heat resistance. The metal rod 40 is removed by moving this rod with approximately rectilinear translational movement radially to the outside of the model. The shape of the metal rod 40 tapering radially to the inner side can effectively reduce the risks of damage to the wax during this extraction operation. The intended purpose of replacing the metal rod 40 with a ceramic rod is to allow the rod to better withstand subsequent casting of the molten metal alloy and to facilitate removal of the rod by a conventional chemical method at the final stage of the manufacturing method, as will be described in more detail below.

The second step 32 of the method ends with step 62 of removing the wax model 50, including the ceramic rod, from the mold.

The method then continues to a third step 34, which includes a step 64 for manufacturing a mold from cement or the like by duplicating the wax model 50 that was previously obtained. More specifically, this wax model 50 is coated with cement so that the cement encloses a protrusion of the ceramic rod contained in this model.

The third step 34 ends with a wax removal step 66 in a conventional manner, including, for example, heating a given wax, in order to obtain a cement mold containing the aforementioned ceramic rod, the protrusion of which is immersed in the mold so as to firmly hold the rod.

The fourth method step 36 includes a step 68 of pouring the molten metal alloy into a preformed cement mold. The rod, placed in the form, allows you to form the corresponding cavity of the blade 18 of the created annular scapular node. The next step 70, after cooling the metal alloy in the mold, consists in removing the blade assembly thus obtained from the mold and removing the ceramic rod by a conventional, preferably chemical, method.

Since during the implementation of the above method, the radially inner end of the rod did not protrude beyond the blade assembly, the inner screen of this assembly does not contain an opening formed by the rod after removing the latter. Thus, the method in accordance with the invention allows to do without the final stage of sealing the inner screen of the annular scapular nodes and can improve the correct form and structure of this screen.

The method in accordance with the invention, as an option, can be implemented without performing step 60 of removing the metal rod and replacing the rod with a ceramic rod. In this case, the entire method is carried out using the same metal rod. In this case, the metal rod has a sufficiently high melting temperature relative to the melting temperature of the poured metal alloy to withstand the high temperatures associated with pouring the molten metal alloy during step 68.

The method in accordance with the invention can be widely used for the manufacture of annular blade assemblies forming a single unit, for example, the assembly described above, or for the manufacture of assemblies formed of a plurality of sectors connected end-to-end in the circumferential direction, each of the sectors including a blade containing an inner cavity, can be manufactured by this method.

Claims (7)

1. A method of manufacturing a wax model (50) of an annular blade assembly (10) of a turbomachine stator for manufacturing a mold for a given blade assembly comprising two coaxial screens, respectively, radially internal (52) and radially external (54) connected to each other by blades (56 ), of which at least one blade (58) has an internal cavity, including the use of a metal shape having approximately the shape that must be given to the said model (50) of the annular blade assembly, the step (38) of placement in the metal the shape of the rod (40), intended to form an impression of the cavity in the area of the metal mold, which forms the blade (58) containing the cavity, and the rod (40) has a predominantly elongated shape containing a radially outer end (42) mounted on the metal the mold, step (48) of injecting the wax into said metal mold containing said rod (40), after cooling said wax, step (62) of removing the formed wax model (50) containing said rod (40) from we, characterized in that the said rod (40) is made of metal and positioned so that its radially inner end (46) is placed on the said section of the form, forming a blade (58) containing the cavity at a distance from the radially inner end of this section forms. 2. The method according to claim 1, characterized in that the said metal rod (40) has a cross section that tapers in the direction of its radially inner end (46). 3. A method of manufacturing an annular blade assembly (10) of a turbomachine stator containing two coaxial screens, respectively radially internal (12) and radially external (14) connected to each other by blades (16), of which at least one blade (18) contains an internal cavity, including:
- a step (32) for manufacturing a wax model (50) of said blade ring assembly (10) by the method according to claim 1 or 2,
- a step (34) for manufacturing a mold from a heat-resistant material by duplication (64) of said wax model (50) followed by removal (66) of the wax,
- a step (68) of pouring the molten metal alloy into said mold made of heat-resistant material and containing said rod (40) to form said annular blade assembly (10),
- after cooling said metal alloy, step (70) of removing said annular blade assembly (10) and removing said rod (40). 4. The method according to claim 3, characterized in that before the step (34) of manufacturing the mold from the heat-resistant material, a step (60) of removing said metal rod (40) from said wax model (50) is carried out, followed by placement in a print formed in wax the said metal rod (40), a rod of the same shape made of ceramic material. 5. The method according to claim 4, characterized in that said heat-resistant material is cement. 6. A metal mold intended for the manufacture according to claim 1 or 2 of a wax model (50) of an annular blade assembly of a stator of a turbomachine containing two coaxial screens, respectively radially inner (52) and radially outer (54) connected to each other by blades ( 56), of which at least one blade (58) contains an internal cavity, and the shape comprises, in the region that forms said blade (58) containing said cavity, a rod (40) of predominantly elongated shape containing radially external to an end (42) mounted on said metal mold to form an imprint of the said cavity, wherein the rod (40) is made of metal and located so that its radially inner end (46) is placed on the said portion of the mold forming the said blade (58), containing said cavity, at a distance from the radially inner end of said portion of the mold. 7. Wax model (50), intended for the manufacture according to claim 3 of an annular blade assembly (10) of a turbomachine stator containing two coaxial screens, respectively radially internal (12) and radially external (14) connected to each other by blades (16 ), of which at least one blade (18) contains an internal cavity, and the model (50) includes in the area (58) that forms the said blade (18) containing the said cavity, the rod (40) is predominantly elongated, containing radially outer end (42), protruding of the aforementioned model (50) in order to form an imprint of the said cavity, wherein said rod (40) is made of metal and located so that its radially inner end (46) is placed on the said section (58) of the model (50) forming the aforementioned a blade (18) containing said cavity at a distance from the radially inner end (52) of said portion (58) of the model (50).

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